1. Field of the Invention
The invention resides in the field of overhead contact systems suspension apparatus and more particularly relates to an apparatus and method used where a contact line is subjected to an abrupt change in line angle at a suspension point such as at the crest or trough of a vertical curve of the associated railway track or roadway but can also be attributed to a required change in contact wire height at low clearance areas such as bridge overpasses or tunnels where the change in contact wire height must be achieved over a relatively short distance.
2. History of the Prior Art
Electrically powered vehicles such as streetcars, trolley buses, light rail vehicles or electric locomotives utilize a current collecting device such as a trolley pole or a pantograph which rides on top of the vehicle and contacts the trolley contact wire of the overhead contact line. Where the overhead contact line must be either lowered or raised in height over a short distance, an abrupt change in direction of the contact wire occurs and the force from this line angle causes the contact wire to be pulled down at the crest of a vertical curve or pushed up at the trough of the vertical curve whether or not the associated track or roadway is vertically horizontal or horizontally curved. The vertical curve rail counteracts the applied forces in the contact wire to hold the wire in a position allowing the current collector to travel along it without erratic movement so that bounce and electrical arcing are prevented. At the crest or trough of a vertical curve the contact wire forms an abrupt angle that the current collector must negotiate. The angle can sometimes be smoothed out using a messenger wire for crests along the curve where the individual catenary hangers or dropper wires attached to it lift the contact wire at close intervals to reduce the overall angle to a series of very small angles that are negotiable for the current collector. At troughs along the curve, for some types of applications, the contact wire is not suspended for several spans so that it sags with a curve of such degree that the current collector can negotiate the curve as the abruptness of angle change is substantially reduced. Another method of smoothing out the trough curve is to add weight to the contact wire so that it has more than normal weight over a short span and sags in a similar manner as the long span and the weight counteracts the lifting force of the angle so that equilibrium is achieved. Where these mitigation methods cannot be employed, the abrupt angle is not allowed to be smoothed out and remains in place through the use of hold down or hold up spans so that an erratic operation of the current collector occurs where bounce, arcing and accelerated wear of the contact wire result. If the speed of the vehicle is great enough, the current collector may skip off the wire at the trough curve or be accelerated upwards at great force at the crest curve causing wear of the contact wire and the rubbing of the surface of the current collector due to increased frictional forces. The contact wire must be held in place at these locations, and either span wires or bracket arms are employed to suspend the wire at the crest of a vertical curve or hold it down at the trough of a vertical curve.
Various inventions in the prior art have addressed these difficulties. For example, U.S. Pat. No. 393,317 to Van Depoele discloses an arched suspender where a bar is attached to an arch, and the bar has an ear attached to it which holds the trolley wire contact line. The bar is flexible only in the horizontal plane where it acts as a pullover to hold the contact wire in position for horizontal curves and does not act in the vertical plane. U.S. Pat. No. 499,167 to Hunter details a trolley wire curve where at curves, the trolley wire is carried about the curve with suitable bends held in place by stay wires also referred to as pulloffs. Directly below the contact wire, a second wire is suspended and is connected to the main wire by ears. The suspended secondary wire acts in the horizontal plane to conform to the angle produced by bending at each pulloff or stay wire and does not act in the vertical plane nor does it provide an elastic suspension because components are rigidly attached. U.S. Pat. No. 584,911 to Westinghouse makes use of a supplemental wire attached to a suspension point and connected to the trolley wire contact line at two points, each on one side of the suspension span. This is done to reduce the angle formed at the suspension point so that the vertical curve at the suspension point is reduced. However, the projected line is level and not at a vertical curve of the track or roadway and the angle produced to which the supplemental wire is allegedly used to reduce is a normal angle produced by the sag of the wire. This invention is not adaptable or compatible with the angle and suspension created at a vertical curve and is designed to keep the trolley wire contact line level and of consistent height rigidly for a fixed vertical trolley pole current collector that is 90 degrees to the contact wire. In U.S. Pat. No. 918,761 to Mayer a trolley wire suspender is disclosed. This device consists of a resilient bar of decreasing cross sectional area to which the trolley wire is rigidly attached through a series of clips that completely encircle the wire. Although the device bends in the horizontal and vertical planes, FIG. 3 and FIG. 4 show clip 4 and clip 7 encircling the contact wire in a manner where the current collector would contact the wire and the clip. Such clips shown in FIGS. 3 and 4 do not allow the use of a trolley wheel or sliding shoe. A variation of these clips is devised, as shown in FIG. 6, for the use of a FIG. 8 or grooved contact wire. Two separate and distinct clip variations must be employed for current collectors to which Mayer refers as a bow or a wheel. This is synonymous with the pantograph or trolley pole current collector of today. Mayer discloses in FIG. 1 a flexible bar that in a preferred embodiment decreases in cross section from the center towards the ends in a manner to achieve an approximately uniform curvature. Due to the greater cross section in the plan and side elevated views at the suspension point referred to as perforated ear 2, the middle point of the device (2) is less flexible than at other points along suspender bar 1 and in fact cannot have equal curvatures along its length due to varying thicknesses of cross section.
In Mayer the trolley wire suspender is attached by one point at 2, as shown in FIGS. 1 and 5 and is designed to act only as a suspender in that the forces applied from the contact wire in a vertical curve pull down and do not push up.
U.S. Pat. No. 2,342,242 to Birch discloses a Conductor Support that is directional in that it is intended for the current collector to travel in one direction only, as described as the approach half A and the leaving half B, and the invention of Birch is intended for normal trolley wire construction with round trolley wire using clinch ears. Birch describes the current collectors making a too abrupt passage from the leaving end of the ear and injuries to the trolley wire result. With Birch, the leaving end B of the clinch ear is altered, as shown in FIG. 8, so that the trolley wire can flex out of the ear as the ear rotates due to the passage of the current collector. Although FIG. 2 shows a vertical angle to the contact wire at the suspension point, it is not due to the overall suspension of the contact wire at the crest of a vertical curve but to the rotation of the clinch ear around a fixed point which is hanger 3 attached to span wire 4. The invention of Birch is not designed for either vertical or horizontal curves of the contact wire but a means to alleviate the wearing out of the contact wire at leaving end B of the clinch ear.
U.S. Pat. No. 499,167 to R. M. Hunter discloses a trolley wire curve where the main wires indicated as C in FIG. 1 carry the tension in the contact line. Around the curve indicated as A, a second or working wire E is suspended under main wire D. The invention is intended to prevent wearing of the main wire as the trolley wheel L runs on the surface of conductor C, F and E but does not touch the main conductor. Hunter further states that by use of this construction, a more rigid and durable curve is produced. Hunter's invention is a device to prevent the wearing of the main contact wire around a conventional curve held in place with standard pullovers. It does not relate to combinations of vertical and horizontal curves of the contact wire but only to holding the conductor in place which has a secondary working conductor suspended from it. The extreme ends of Wire E have inclined castings F which join working wire E to main wire D. The slope produced by this casting F can be of sufficient gradient to cause a pantograph to skip off the wire due to speed and cause an electric arc on the wire. Arcing will degrade the cross section of the wire, leading to accelerated wear and fracture.
U.S. Pat. No. 2,491,973 to R. P. Hanna discloses a Conductor Support in which the device is designed to act as a pulloff for contact wires in curved segments. The disclosed invention is designed for contact wire pulloffs on curves in the horizontal plane only and cannot be adapted for use as a vertical conductor support as the conductor support member 14 has trolley wire clamps 15 attached to it in a horizontal orientation. The adjustability of the device for various curve angles has a preset range as indicated in FIG. 1 by solid pictorial lines and broken pictorial lines. The device cannot be used at zero degrees or any combination from zero to the preset minimum angle. Angle variations, once the device is set, cannot be accommodated without making an adjustment to tension member 30 which adjustment is accomplished by loosening nuts 33 on threaded end portion 32 to let the rod out slightly from opening 28 on pulloff means 17.